Phillips, 53, of Underhill, Vt., is captain of the Maersk Alabama, a 17,000-ton container ship carrying relief aid to Mombasa, Kenya. On Wednesday, the ship was attacked by Somali pirates. While the unarmed crew repelled the initial attack, Phillips reportedly prevented a bloody counterattack by the pirates by offering himself as a hostage.

Phillips' actions, while heroic, were also exceedingly dangerous -- and they also opened up serious questions when it comes to the natural human motivation of self preservation, said Dr. Charles Raison, assistant professor in the Mind-Body Program at the Emory University School of Medicine's Department of Psychiatry and Behavioral Sciences

"These stories, this tendency to do this sort of thing, it often surprises people from a scientific point of view," Raison said.

But, he added, "Some theorists say that this is one of the reasons that we as humans have emotions. It is one way to get humans to transcend the simple arithmetic of self interest."

Ben Sherwood, author of the bestselling book "The Survivors Club" and a former executive producer of ABC News' "Good Morning America," has interviewed survivors around the world, including hostages and prisoners of war. In his research, he has come across a phenomenon he has termed the "10-80-10" rule.

"Ten percent of us, in a crisis, will respond as leaders with clear heads, with purposefulness, and will do things to save ourselves and save others," he said. "Eighty percent of us will become bewildered. ... We freeze and we wait for someone to tell us what to do."

The final 10 percent will become self-destructive, he said. But the heartening news, he said, is that most of us at least have the potential to act in a heroic manner.

"An easygoing, calm, collected mind helps you be in that [top] 10 percent," he said. "The key is how to flip the switch from being in the 80 percent into the 10 percent."

Raison agreed.

"This ability to sometimes make a heroic sacrifice for one's fellow man is rather hardwired in human beings. Some people are not like this; in times of a crisis, they will sell everyone else downstream."

The following pages feature a few examples in recent years of heroes -- as well as those who have not acted so heroically.

Capt. Richard Phillips

But even if Phillips knew of the risks, could he have guessed how well he would react when pirates attacked his vessel?

By the descriptions he's read, Sherwood said, Phillips could possibly fall into the profile of the natural survivor.

"He's been described by his friends and family as smart and easygoing," said Sherwood.

Yet, Sherwood points out that the crew had one of the most important advantages for dealing with a crisis situation: training.

The father of the second-in-command of the Maersk Alabama told the Associated Press that his son, Shane Murphy, went through anti-piracy tactics training before going into dangerous waters.

"Training is essential in surviving and thriving in a crisis," said Sherwood. "People who have trained for adversity are better prepared to overcome it. We know this from all kinds of research."

In Phillips' case, his training allowed him to save the crew at the risk to his own personal safety. But not all captains have acted in the same manner in the past. Such was the case in 1991, when the Greek linker Oceanus encountered bad weather and began to sink off the coast of South Africa.

Capt. Yiannis Avranas reportedly shouted "abandon ship" to his crew and 170 passengers on board. Then, according to reporting by the Chicago Sun-Times, Avranas shoved and elbowed women and the elderly to get on the rescue helicopter first.

"When I ordered 'Abandon the ship,' it doesn't matter what time I leave," the Sun-Times reported he said in one interview. "Abandon is for everybody. If some people like to stay, they can stay."

Fortunately, all 561 people on board made it to shore safely -- even if Avranas' reputation did not survive.

For the most part, Sherwood said, Avranas is the odd captain and the odd man out.

"The myth of survival situations is that it's every man or woman for themselves and that people engage in animalistic, dog-eat-dog behavior," he said.

Most research Sherwood found indicated that people naturally bind together in the face of adversity, whether it be a community in a hurricane or the community of 20 sailors at sea.

"There will always be exceptions," said Sherwood. "There will always be a captain who jumps off a ship. There will always be the person who makes a run for it."

Flying over Manhattan's looming skyline, Sullenberger calculated it would be better to ditch the plane in the Hudson River than to fly straight ahead to the nearest runway in New Jersey and risk losing power.

Not only did he successfully land and evacuate all 155 passengers on a cold January day, Sullenberger walked down the plane's aisle twice checking for stragglers before he exited the plane.

"He had a lot of training," said Sherwood, who studied the Sullenberger case. "He practiced what he knows in his field as 'deliberate calm.'"

Not only can people train for a specific situation, Sherwood said, people can undergo training to focus their emotions and thoughts to in order handle any survival situation.

"The enemy of survival is panic and stress and anxiety," said Sherwood.

In addition to learning calm, Sherwood said, those who aren't natural-born survivors can also learn a behavior called "active-passiveness" -- meaning knowing when to act and when not to act in survival situations.

Sullenberger might just be the definition of a survivor, considering his performance with the technical training to land the plane, the calm thinking to make a decision, and the ability to decide whether he should act and ditch the plane instead of pushing to the nearest airport.

Neal Beidleman and Other Survivors of a Mount Everest Tragedy

Any climb on Mount Everest is a test of human survival. But the events of May 10 and 11, 1996 included some of the most harrowing, heroic and controversial tales of survival on the world's highest mountain.

About 30 climbers attempted to ascend on May 10, which started out as a picture-perfect clear day, according to reporting in Outside magazine. But a severe storm described by the climbers as a wintery "hurricane" came on by late afternoon, just when the climbers needed to descend in order to make it back to camp safely.

The tragic day made several guides into heroes. Expert climbers Neal Beidleman, Rob Hall, Andy Harris, Scott Fischer and Anatoli Boudreev all as risked their lives to save others -- and some lost their lives in the process.

Those days, and some key disputed decisions that some argue could have saved lives, have inspired books "The Climb" by Anatoli Boukreev and Gary Weston DeWalt, "Left for Dead" by climber Beck Weathers, "Mountain Madness" by Robert Birkby, "Into Thin Air," by climber Jon Krakauer and several movies.

Many fingers have been pointed and aspects of the case discussed in letters to Outside magazine. But one of the largest issues was whether world-class climber Anatoli Boudreev, who ventured out into deadly winds to save two climbers, should have acted differently earlier in the day.

Whatver the controversy, experts say the fact that so many acted altruistically was actually part of human nature.

"There's something called the diffusion of responsibility," said Cleveland Clinic psychologist Scott Bea, referring to the so-called 'bystander effect.'

Although people can refrain from taking responsibility to act to save one in danger, as in the bystander effect, Bea said, when an entire group is in danger the opposite can happen: People feel a sense of allegiance and act with courage they may not have had alone.

"We can often behave with greater courage, and we feel more compelled to do so if a group is acting bravely than if we were in isolation," Bea said.

Leonard Abess Jr.

At a time when most banking CEOs are embroiled in controversy over multi-million-dollar bonuses and golden parachutes, Leonard Abess Jr. stood out by offering his employees $60 million out of his own pocket.

It was an act that many described as heroic and that even was acknowledged by President Barack Obama during a speech to Congress on Feb. 25, 2009.

"I think about Leonard Abess, the bank president from Miami who reportedly cashed out of his company, took a $60 million bonus, and gave it out to all 399 people who worked for him, plus another 72 who used to work for him," Obama said in his speech.

"It was an amazing moment," Abess told ABC News' Alice Maggin. "I was humbled and amazed; it was really something."

While Abess' sacrifice was not technically a life-or-death decision, Raison said that the altruism he displayed is similar to that shown by those in more perilous situations.

"I think that in all of these cases, what we see is that there is clearly a facet of human nature where, when the chips are down, some people are willing to sacrifice themselves for the greater good," Raison said.

The recognition Abess received stands in stark contrast to the lambasting of Merrill Lynch CEO Jon Thain, who became a poster boy for corporate greed when the national news media discovered that he had spent more than $1.2 million to redecorate his office, even as his firm lost $8 billion and was preparing to lay off 10 percent of its work force.

According to Charlie Gasparino, CNBC's on-air editor, who broke the story, the money Thain spent, in part, went for two area rugs ($131,000), two guest chairs ($87,000), a 19th Century credenza ($68,000), four pairs of curtains ($28,000), and a mahogany pedestal table ($25,000). Also reported to be on the list was a trash can for $1,400.

Thain's attorney has since told ABC News' Richard Esposito that Thain has agreed to reimburse the company for those charges.

Despite being the counterweight to such high-profile episodes, Abess said he was was surprised at the attention his gesture had received.

"I'd prefer to live in a world where this is ordinary and didn't need to be mentioned to anybody," Abess told Maggin.

Todd Beamer

Stories of selfless heroism were in no short supply in the days following the Sept. 11, 2001 terrorist attacks. Perhaps one of the most inspiring was that of Todd Beamer, 32, who was a passenger on United Flight 93 when it was hijacked.

Together with fellow passengers Jeremy Glick and Mark Bingham, Beamer helped coordinate a last-ditch effort to retake the plane once they learned that it might be used as a missile to destroy yet another American target on the ground. Beamer reportedly was the passenger who was heard uttering the words, "Let's roll," by a telephone operator with whom he had been talking before the passengers presumably stormed the cockpit.

The plan may have succeeded. Of the four flights hijacked by terrorists that day, Flight 93 was the only one that did not crash into a populated target. Tragically, however, the plane did crash, killing all aboard.

Lisa Beamer, the wife of Todd Beamer, told ABC News' "Good Morning America" two months after the crash that she believed the men's primary goal was to save those on the ground -- even if it meant sacrificing their own lives in the process.

"I think they succeeded in their mission to save the people on the ground and were this close to saving themselves," she said.

"In this case, the most altruistic thing they might have been doing was to take the plane down because they knew it was heading somewhere bad that would have gotten more people killed," Raison said.

He added that the ramifications of Beamer's actions -- as well as the actions of other self-sacrificing heroes -- went far beyond the moment in which they were carried out.

"One thing that is really cool about altruistic behavior is that it spreads. It's contagious," Raison said. "So one act can have big ramifications."

And he said the most heartening impact of such sacrifices is that they may say something about the capacity of all people to be heroes.

"The seeds for what these people have done are in all of us," Raison said. "The evolution of this type of behavior is part of what makes us human."

Reports from Russell Goldman, Alice Maggin and Richard Esposito contributed to this story.